Remove useless `touch` line

test/prefix.bats

@@ -26,7 +26,6 @@ load test_helper
 
 @test "prefix for system in /" {
   mkdir -p "${BATS_TEST_DIRNAME}/libexec"
-  touch "${BATS_TEST_DIRNAME}/libexec/rbenv-which"
   echo "echo /bin/ruby" >"${BATS_TEST_DIRNAME}/libexec/rbenv-which"
   chmod +x "${BATS_TEST_DIRNAME}/libexec/rbenv-which"
   RBENV_VERSION="system" run rbenv-prefix